xref: /freebsd/lib/libsys/close.2 (revision 053a988497342a6fd0a717cc097d09c23f83e103)

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.Dd December 18, 2024
.Dt CLOSE 2
.Os
.Sh NAME
.Nm close
.Nd delete a descriptor
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn close "int fd"
.Sh DESCRIPTION
The
.Fn close
system call deletes a descriptor from the per-process object
reference table.
If this is the last reference to the underlying object, the
object will be deactivated.
For example, on the last close of a file
the current
.Em seek
pointer associated with the file is lost;
on the last close of a
.Xr socket 2
associated naming information and queued data are discarded;
on the last close of a file holding an advisory lock
the lock is released (see further
.Xr flock 2 ) .
However, the semantics of System V and
.St -p1003.1-88
dictate that all
.Xr fcntl 2
advisory record locks associated with a file for a given process
are removed when
.Em any
file descriptor for that file is closed by that process.
.Pp
When a process exits,
all associated file descriptors are freed, but since there is
a limit on active descriptors per processes, the
.Fn close
system call
is useful when a large quantity of file descriptors are being handled.
.Pp
When a process forks (see
.Xr fork 2 ) ,
all descriptors for the new child process reference the same
objects as they did in the parent before the fork.
If a new process is then to be run using
.Xr execve 2 ,
the process would normally inherit these descriptors.
Most
of the descriptors can be rearranged with
.Xr dup2 2
or deleted with
.Fn close
before the
.Xr execve 2
is attempted, but if some of these descriptors will still
be needed if the execve fails, it is necessary to arrange for them
to be closed if the execve succeeds.
For this reason, the call
.Dq Li fcntl(d, F_SETFD, FD_CLOEXEC)
is provided,
which arranges that a descriptor will be closed after a successful
execve; the call
.Dq Li fcntl(d, F_SETFD, 0)
restores the default,
which is to not close the descriptor.
.Sh RETURN VALUES
.Rv -std close
.Sh ERRORS
The
.Fn close
system call will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument
is not an active descriptor.
.It Bq Er EINTR
An interrupt was received.
.It Bq Er ENOSPC
The underlying object did not fit, cached data was lost.
.El
.Pp
In case of any error except
.Er EBADF ,
the supplied file descriptor is deallocated and therefore is no longer valid.
.Sh SEE ALSO
.Xr accept 2 ,
.Xr closefrom 2 ,
.Xr execve 2 ,
.Xr fcntl 2 ,
.Xr flock 2 ,
.Xr open 2 ,
.Xr pipe 2 ,
.Xr socket 2 ,
.Xr socketpair 2
.Sh STANDARDS
The
.Fn close
system call is expected to conform to
.St -p1003.1-90 .
.Sh HISTORY
The
.Fn close
function appeared in
.At v1 .